The gastrointestinal tract comprises a mucosal surface which is submitted to aggressive secretions and/or body forces involved in the digestion. In the stomach, the digestion is obtained by the secretion of the acid gastric juice. Presently available methods to evaluate in man the aggressive and damaging powers of digestive secretions are based on intraluminal pH measurements or on biochemical assays. Intraluminal pH measurements yield an instantaneous measure of the acidity of the gastrointestinal contents at a given location in the gastrointestinal tract. Biochemical assays measure in vitro parameters such as enzyme activities in an amount of digestive juices collected over a given period of time. These approaches only allow to measure instantaneous changes in parameters which are known or assumed to have a role in the production of tissue damages.
Examples of intraluminal pH-sensing electrodes are glass or plastic electrodes, ISFET (Ion Sensitive Field Effect Transistor) optical electrodes, combination electrodes or unipolar monocrystalline antimony electrodes (connected to a pH-meter via a cable).
The reference "Chemical Sensors based on Fiber Optics", Analytical Chemistry 56(1), 16A-34A, W. R. Seitz, Easton U.S. (1984) describes devices involving a reagent phase on the end of an optic fiber. In operation, interaction with analytes leads to a change in optical properties of the reagent phase, which is probed and conducted through the optic fiber.
In particular, a class of irreversible sensors is described. The "irreversible" sensing principle, in the sense of a reagent consuming system, is based on analytical reactions that consume reagent. Said "irreversible" sensors can have a lifetime of months, or years but act within said lifetime as reversible systems with respect to sensor response. Said reversibility means that whenever said "irreversible" sensor is transferred from a first medium, e.g. with oxygen partial pressure (a), to a second medium with oxygen partial pressure(b), and thereafter back to said first medium, said sensor back in the first medium will again record an oxygen partial pressure.
The document "Research on Gastric Multiparameter Sensors Technology", Proceedings of ICEE Engineering in Medicine and Biology Society, vol. 14, 16-120, X. Lin et al. (1992) introduces gastric multiparameter sensor technology and describes devices based on reversible measurement principle.